Triarylmethyl indicator compounds that detect the presence of acidic molecules are useful, for example to detect the presence of bacteria in foods, wounds, and the like. To detect bacterial growth, the indicator is included in a polymeric matrix that contacts, for example, the wound or the food. If the indicator is not covalently bound to the polymeric matrix, there is a possibility that the indictor can leach out of the polymeric matrix and mix with the food or wound. While this problem can be addressed by cross-linking the polymer to entrap the indicator, there are many examples where the polymers are not desirably cross-linked. Moreover, cross-linking is not an absolute assurance that a small amount of the indicator will still not leach.
Hexamethoxy red and heptamethoxy red are preferred pH indicators as they are transparent at pH's of about 6 and above, and bright red/purple at lower pHs. The use of such indicators is beneficial as it provides an accurate visual analysis of the presence of bacterial growth. While there exists numerous ways to modify pH indicators to include a polymerizable group, it is essential that such modification does not significantly alter the pKa of the so modified indicator so that the indicator retains its underlying detection characteristics. Provided here are triarylmethyl indicators which can detect a wide range of acidity, and/or that comprise one or more polymerizable groups. These polymerizable groups are introduced in such a manner that the pKa of these indicators is not materially altered.